The present invention relates generally to a positioning platform mechanism for a spacecraft. More particularly, the present invention relates to a two-axis positioning mechanism for a spacecraft that utilizes a single motor.
Positioning mechanisms, including two-axis positioning mechanisms are utilized on most current spacecraft. These positioning mechanisms are used to steer antennas, thrusters, momentum wheels and other devices requiring repositioning or realignment. Many current positioning platform mechanisms suffer from a variety of disadvantages.
Many positioning mechanisms utilize two or three or more motors in order to effectuate repositioning or realignment. This adds weight to the spacecraft, thus increasing its cost and also potentially decreasing the reliability.
Additionally, most of the current positioning mechanisms are heavy and/or relatively complex. Moreover, all current positioning mechanisms require a redundant system in the event the main positioning mechanism fails. It is a common practice to provide redundancy in these positioning mechanism. The redundant features may be either electrical or mechanical. Current mechanically redundant mechanisms use heavier, more complicated differential drives, floating gear drives (see for example U.S. Pat. No. 4,858,490), or three motor tripod platforms. For example, a typical redundant differential gear drive uses two motor drives per axis, for a total of four motors. These devices have complicated drive trains and are expensive and heavy.
Positioning mechanisms are also used for other applications including solar array systems in order to perform deployment and sun tracking functions. These positioning mechanisms also suffer from similar disadvantages to those outlined above. Therefore, it would be advantageous to develop an inexpensive, light, positioning mechanism that has a reliable redundant system.
Accordingly, it is an object of the present invention to provide a positioning mechanism that is lighter, smaller, less complex, and less expensive than prior positioning mechanisms.
It is a further object of the present invention to provide a positioning mechanism that has improved reliability over prior positioning mechanism.
It is a related object of the present invention to provide a positioning mechanism that has fewer electrical components and connections than prior systems.
In accordance with these and other objects of the present invention, a two-axis positioning mechanism is provided. The two-axis positioning mechanism includes a motor that effectuates the steering about a first axis and a second axis. The motor has a pinion attached to a drive shaft that simultaneously drives a first drive and a second drive. The first drive includes a first gear, a first worm shaft in communication with the first drive gear at a first end, and a first worm on the first worm shaft. The first worm communicates with a first worm wheel mounted on an output shaft. The output shaft includes a first output cam mounted thereon which effects positioning about the first axis. The second drive includes a second gear, a second worm shaft in communication with the second drive gear at a first end, and a second worm on the second worm shaft. The second worm engages a second worm wheel mounted on an output shaft. The output shaft includes a second output cam mounted thereon which effects positioning about the second axis. The first ends of each of the first worm shaft and the second worm shaft are in rotational communication with their respective drive gears through respective one-way torque transmission devices.
These and other features and advantages of the present invention will become apparent from the following description of the invention when viewed in accordance with the accompanying drawings and appended claims.